Later generations of cellular communication networks are renowned for their complexity. A large amount of wireless devices and User Equipment's should be able to communicate with each other and with relevant network nodes as seamless as possible. The complexity related to the management of such networks has created an urge to design network solutions where the demands on management are softened. As an example, the evolvement of Self-Organized Networks, SONs, has become an important feature to achieve such a simplification of network management. The development of SONs is, beside the potentially overarching aim to reduce the complexity, also important when considering the need for heterogeneous networks and for optimizing, e.g. Wideband Code Division Multiple Access, WCDMA, Radio Access Network, RAN, for the next wave of mass-market operators.
An important feature in modern and future cellular communication networks, in general, and the development of SONs, in particular, is related to the management of neighbor cell relations. The management of neighbor cell relations can be seen as an important cornerstone in order to achieve efficient Self Organized Networks, SON. Moreover, if such neighbor cell relations can be automatically generated this would, aside from lowering installation and operation costs for operators, also improve the Key Performance Indicator, KPI, called retainability. The technology behind automatically generated neighbor cell relations is generally referred to as Automatic Neighbor Relations, ANR, and such neighbor cell relations are often maintained in one or more databases; for example in a neighbor cell list or, equivalently, a neighbor cell table or other suitable representation.
It would be highly desirable if a network node had an at least satisfactory knowledge about the neighbor cell relations between the cells within the network since this would make a lot of the operations that are managed by, or under the control of, the network node more robust. For example, some standardized network solutions even require information of neighbor cell relations for proper network operation. A possible example of an operation that would benefit from neighbor cell information is the handover of a User Equipment between different cells. Knowledge about neighbor cell relations would, for example, reduce the amount of dropped calls during handover. It would also facilitate the management of the network, for example, by making manually performed additions of neighbor cell relations more or less redundant. Since a cellular communication network in general is gradually evolving over time, new neighbor cells will frequently be added to the cellular communication network and new interference patterns among the cells will emerge. In order for the network node to maintain relevant information about neighbor cell relations, measures are needed that will enable a network node to update its knowledge about neighbor cell relations between cells through the means of detecting missing neighbor cell relations.
A problem is that manual configuration of neighbor cell relations takes a lot of time for operators. In light of this, the design of efficient mechanisms that are able to automatically detect missing neighbor cell relations has become increasingly important and several different measures have been proposed.
In one of the known methods, the User Equipment, UE, reports detected cells to the Radio Network Controller, RNC. The RNC may order the UE to measure and report missing cells, i.e. cells that are not already defined in a neighbor cell list. The order is sent to the UE in a MEASUREMENT CONTROL message together with other measurement control information such as event/reporting criteria, neighbor cell list, measurement quantities, and measurement command(s). The UE will apply the same measurement control information on all cells, i.e. both detected set cells and cells listed in a neighbor cell list. If a detected set cell triggers a measurement event the UE will send a MEASUREMENT REPORT message to the RNC. The RNC will evaluate the MEASUREMENT REPORT message to find out if the reported cell is already defined as a neighbor or not. If not, it can be added as a new neighbor relation.
However, this method does not work for certain radio access technologies and cells such as GSM cells, since detected set reporting for GSM cells, for example, does not exist.
ANR logging has been proposed as an optional feature to detect missing neighbor relations [1]. When the feature is activated the User Equipment, UE, will measure and record detected set cells in Idle mode, UTRAN Registration Area Paging Channel, URA_PCH, state and Cell Paging Channel, CELL_PCH, state. The report can be retrieved by the Radio Network Controller, RNC, when the UE becomes active, i.e. when the UE is in Cell Dedicated Channel, CELL_DCH, and Cell Forward Access Channel, CELL_FACH, state. Each report contains up to four missing relations detected by the UE. The UE may log and report Intra-frequency, IAF, Interfrequency, IEF, Long Term Evolution, LTE and Global Systems for Mobile communications, GSM, relations.
As indicated, the UE support for ANR logging is an optional 3GPP feature and thus it is difficult to predict how many UEs that will actually support ANR logging in the future.
Another possible method to find GSM neighbor cells relates to GSM and measurements on unknown cells, so-called “ghost cells”. The UE is then ordered to measure on unknown cells not defined as neighbor relations, but with possible combinations of Broadcast Control Channel, BCCH, and Base Station Identity Code (BSIC) that exist in the network. If the UE measure on “ghost cell” but finds and reports a real cell, a new neighbor relation can be defined to this cell from the source cell. Although this solution could work quite satisfactory, there is still room for improvements.
WO 2014/011091 relates to a technique for updating neighbor cell relations in a cellular communication network. A User Equipment, UE, switches from being served in a source cell by a source base station to being served in a target cell by a target base station. The UE sends an identifier of the source cell and a request for a mobility report to the target base station. The target base station sends a mobility report to the source base station. The mobility reporting that a successful switch has taken place between the source cell and the target cell enables updating of the neighbor cell relations based on the mobility report.